Supported catalyst and method for preparing the same

ABSTRACT

The invention provides and a highly-dispersed supported catalyst that has a reduced average particle size of catalytic metal particles and is also supported by a porous support material. A method of preparing a supported catalyst that can reduce the average particle size of catalytic metal particles supported by a support material includes first mixing a charged support material with a solution containing a polymer electrolyte having a charge opposite to that of the support material to adsorb the polymer electrolyte on the support material. Next, the support material having the polymer electrolyte adsorbed thereon is mixed with a solution containing a catalytic metal precursor ion having a charge opposite to that of the polymer electrolyte to adsorb the catalytic metal precursor ion on the support material having the polymer electrolyte adsorbed on it. Finally, the catalytic metal precursor ion adsorbed on the support material having the polymer electrolyte adsorbed thereon is reduced to a catalytic metal in a reducing solution.

BACKGROUND OF THE INVENTION

This application claims the benefit and priority of Korean PatentApplication No. 2004-19625 under 35 U.S.C. §119, filed on Mar. 23, 2004,with the Korean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a catalyst and a method of preparingthe same. More particularly, the present invention describes a supportedcatalyst and a method of preparing the same.

DESCRIPTION OF THE RELATED ART

Supported catalysts are widely used to accelerate the chemical reactionrate in various applications. It is well known that a supported catalystconsists of a catalyst component and a porous support materialcomponent. The catalyst component is attached to a surface of the poroussupport material component. In general, since many pores are present ina porous support is material, the porous support material has a verylarge surface area. Such a large surface area provides many positions inwhich many catalyst particles can be dispersed.

For example, a carbon-supported metal catalyst uses a porous carbonparticle as a support material and a catalytic metal particle as acatalyst. Such a carbon-supported metal catalyst is used in an electrodeof a fuel cell. More specifically, a carbon-supported metal catalyst isused in a cathode and/or an anode in a phosphoric acid fuel cell (PAFC),a proton exchange membrane fuel cell (PEMFC), or a direct methanol fuelcell (DMFC).

The catalyst accelerates the rate of electrochemical oxidation of a fueland/or the rate of electrochemical reduction of oxygen. The carbonparticle of the carbon-supported metal catalyst has a dual role as asupport material and as an electronic conductor. Platinum andplatinum/ruthenium alloy, for example, are frequently used as acatalytic metal particle.

Typically, a supported catalyst is prepared by adding a catalytic metalprecursor solution to a dispersion of support material so that thecatalytic metal precursor adsorbs onto the support material. Then asolution of a reducing agent is added to the dispersion to reduce thecatalytic metal precursor adsorbed on a surface of the support materialto a catalytic metal particle (see, U.S. Pat. No. 5,068,161). Finally, afreeze-drying is performed to obtain supported catalyst powders.

It is well known that one of main factors that affect the catalyticactivity of a supported catalyst is the total surface area of supportedcatalytic metal particles. The surface area of the catalytic metalparticles is, in turn, affected by the average particle size ofcatalytic metal particles and the amount of the catalytic metalparticles present on the support. If the amount of the catalytic metalparticles on the support is constant, the average particle size of thecatalytic metal particles is inversely proportional to the total surfacearea of the supported catalytic metal particles. If an average particlesize of the catalytic metal particles is constant, the amount of thecatalytic metal particles on the support is directly proportional to thetotal surface area of the supported catalytic metal particles.

Thus, one of the important technical objects in the supported catalystfield is to produce smaller supported catalytic metal particles than aconventional supported catalyst.

In a fuel cell such as a PAFC, PEMFC, or DMFC, as the activity of acarbon-supported metal catalyst contained in the electrode increases,the power density of electricity generation in the fuel cell increaseswhile maintaining energy efficiency. Accordingly, the ratio of powergeneration to production costs of the fuel cell stack increases and theratio of power generation to the weight or volume of the fuel cell stackincreases.

For a supported catalyst prepared using the conventional method, as theamount of the catalytic metal particles on a support increases, theaverage particle size of the catalytic metal particles tends to increaseas well. Due to this phenomenon, there is a limit on the improvement ofthe catalytic activity of a supported catalyst.

Further, although the size of the catalytic metal particles on thesupport can be reduced by preparing them according to the conventionalmethod, the decrease of the average particle size of the catalytic metalparticles also has a limit.

Thus, there is a need to develop a technique that can reduce the averageparticle size of catalytic metal particles to be placed on a supportmaterial while increasing or maintaining the conventional amount ofcatalytic metal particles supported.

SUMMARY OF THE INVENTION

The present invention provides a method for preparing a supportedcatalyst that can reduce the average particle size of supportedcatalytic metal particles.

The present invention also provides a supported catalyst that has areduced average particle size of catalytic metal particles supported ona porous support material.

An embodiment of the present invention provides a method of preparing asupported catalyst, where a charged support material is mixed with asolution containing a polymer electrolyte having a charge opposite tothat of the support material, thereby adsorbing the polymer electrolyteon the support material. Next, the polymer electrolyte adsorbed on thesupport is mixed with a solution containing a catalytic metal precursor.The charge of the catalytic metal precursor ion is opposite to that ofthe polymer electrolyte the catalytic metal precursor ion on the supportmaterial having the polymer electrolyte adsorbed thereon. Finally, thecatalytic metal precursor ion adsorbed on the support material havingthe polymer electrolyte adsorbed thereon is reduced to a catalytic metalin a reducing solution.

In the present embodiment, prior to adsorbing the catalytic metalprecursor on the support material having the same charge as that of thecatalytic metal precursor, the polymer electrolyte with a chargeopposite to that of the catalytic metal precursor and the supportmaterial is adsorbed on the support material. That is, the catalyticmetal precursor is not adsorbed directly on the support material, but ona layer of the polymer electrolyte adsorbed on a surface of the supportmaterial.

Since the polymer electrolyte has an opposite electrical charge fromthat of the catalytic metal precursor ion, an electrical attractionoccurs between the polymer electrolyte and the catalytic metal precursorion. Thus, the catalytic metal precursor ions are dispersed uniformlyand densely on the surface of the support material having the polymerelectrolyte adsorbed thereon. Surprisingly, the average particle size ofcatalytic metal particles reduced from such catalytic metal precursorion is even smaller than that of supported catalytic metal particles inconventional supported catalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings.

FIG. 1 is a view illustrating the results of an X-ray diffraction (XRD)analysis for a supported catalyst prepared according to example of thepresent invention.

FIG. 2 is a view illustrating the results of an XRD analysis for asupported catalyst prepared according to another example of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the method according to an embodiment of the presentinvention will be described in more detail.

An exemplary embodiment of the present invention provides a method forpreparing a supported catalyst in which a negatively charged supportmaterial is first mixed with a positively charged polymer ion-containingsolution to adsorb the polymer ion on the support material. Next, thesupport material with the polymer ion adsorbed on it is mixed with anegatively charged catalytic metal precursor ion-containing solution sothat the catalytic metal precursor ion can be absorbed on the supportmaterial having the polymer ion adsorbed on it. Finally, the catalyticmetal precursor ion that is adsorbed on the support material having thepolymer ion adsorbed thereon is reduced to a catalytic metal in areducing solution.

Examples of the negatively-charged support material used in the presentembodiment include a carbon-based porous support material, SiO₂-basedporous support material, TiO₂-based porous support material, andV₂O₅-based porous support material.

Examples of the carbon-based porous support material may include, butare not limited to, carbon black, carbon molecular sieve, carbonnanotube, and mixtures thereof. Examples of commercially availablecarbon-based porous support material include vulcan XC-72, Ketjen black,Denka Black, and acetylene black.

In the present embodiment, the support material can be used in powder orsuspension form. The suspension contains a support material and adispersion medium. Examples of the dispersion medium include water,isopropyl alcohol, ethanol, methanol, and mixtures thereof.

The term “polymer electrolyte” refers to a polymer having a dissociationgroup in its backbone or branch. When the dissociation group of thepolymer electrolyte is dissociated, the polymer electrolyte isdecomposed into a low weight ion and a high weight ion. The high weightion inherits the chain structure of the polymer electrolyte and isreferred to as “a high molecular weight ion.”

The positively-charged polymer ion can be derived from a cationicpolymer. Examples of the cationic polymer include, but are not limitedto, a polymer having a nitrogen atom in its backbone or branch. Thenitrogen atom can form an amine structure

or an ammonium structure

The amine structure can be converted to an ammonium structure underappropriate conditions.

Other examples of the cationic polymer include poly L-lysin (PLL),pAMEAMA dendrimer, poly(L-glutamic acid) (PLGA),poly(1-methyl-2-vinylpyridine) (PVP), poly L-ornithine, polyspermine,and diethylaminoethyl dextran (DEAE dextran).

Examples of the cationic polymer electrolyte having a nitrogen atom inits backbone or branch include polyallylamine hydrochloride (PAH),polyethylenimine (PEI), polydiallyldimethylammonium chloride,polymethacryloxyethyltrialkylammonium halide, aminoethylatedpolyacrylamide, Hofman-degradated polyacrylamide, polyethyleneamine,cationized starch, chitosan, and mixtures thereof.

The cationic polymer electrolyte having a nitrogen atom in its backboneor branch may have a repeating unit, as follows:

wherein X is a halogen atom.

The cationic polymer electrolyte with a nitrogen atom in its backbone orbranch may be a copolymer with at least two repeating units describedabove.

If the average molecular weight of the polymer ion or the polymerelectrolyte is too low, it cannot sufficiently surround the carbonsupport material. Thus, platinum complex ions are locally arrangedaround the carbon support material which results an increase in themetal particle size. If the average molecular weight of the polymer ionor the polymer electrolyte is too high, it envelopes the carbon supportmaterial. Thus, a reaction surface area may be significantly reducedeven when the platinum is supported by the carbon support material.

Therefore, the polymer ion or the polymer electrolyte preferably has anaverage molecular weight in a range of about 50 to 15,000. The specificmolecular weight range varies depending on the polymer ion or thepolymer electrolyte. For example, PAH may preferably have an averagemolecular weight in the range of about 5,000 to about 15,000, and morepreferably in the range from about 8,000 to about 11,000. PEI maypreferably have an average molecular weight of about 50 to about 15,000,and more preferably from about 50 to about 5,000.

Examples of a solvent that can dissolve the polymer electrolyte mayinclude but are not limited to water, n-hexane, ethanol, triethylamine,tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), ethyl acetate,isopropyl alcohol, acetone, acetonitrile, benzene, butyl alcohol,chloroform, diethyl ether, and mixtures thereof.

In the present embodiment, a negatively-charged support material ismixed with a positively-charged polymer ion-containing solution toadsorb the polymer ion onto the support material. The polymerion-containing solution may be obtained by dissolving a polymerelectrolyte in a solvent. The support material added to the polymerion-containing solution may be in a form of a powder or a suspension.

The support material may be mixed with the polymer ion-containingsolution using a conventional stirrer, such as a homogenizer and amagnetic stirrer. Through the mixing, the polymer ion becomes adsorbedon the surface of the support material.

The amount of each component in the mixture of the support material andthe polymer ion-containing solution is not specifically limited.However, if the amount of the support material in the mixture isinsufficient, the yield is low and it is difficult to remove the polymerelectrolyte. If the amount of the support material in the mixture is toohigh, the polymer electrolytes can cover all the support material.Considering this, the amount of the support material in the mixture maybe in the range of 0.4% to about 0.5% by weight of total solvents in themixture.

If the amount of the polymer ion in the mixture is too low, there may beinsufficient dispersion. If the amount of the polymer ion in the mixtureis too high, the reaction area of the supported catalyst can be reduced.Considering this, the amount of the polymer electrolyte added to themixture may range from about 5% to about 90% by weight of total solventsin the mixture.

The stirring time of the mixture of the support material with thepolymer ion-containing solution is not specifically limited. However, ifthe stirring time is too short, the polymer ion may be locally arrangedaround the support material. If the stirring time is too long, aproduction process is too time-consuming. The stirring time can varydepending on process conditions, such as performance of a stirrer andamounts of materials to be added. Generally, the stirring time may befrom about 1 hour to about 2 hours.

After the polymer ion is adsorbed on the surface of the support materialin this way, it is mixed with a negatively charged catalytic metalprecursor ion-containing solution. This allows the support materialhaving the polymer ion adsorbed thereon to absorb the catalytic metalion on it. The support material with the polymer ion adsorbed on it maybe mixed with the catalytic metal precursor ion-containing solution bybeing stirred as in the previous operation, using a conventionalstirrer, such as a homogenizer. Alternatively, it can be obtained as aproduct separated by filtering the mixture. Through the mixing, thecatalytic metal precursor ion in the mixture becomes adsorbed on thesurface of the support material having the polymer ion adsorbed thereon.

The negatively charged catalytic metal precursor ion may be an atomicgroup containing a metal atom, such as Pt, Ru, Au, Pd, Rh, Ir, Os, orthe like, or mixtures of the atomic group. The ion may also be derivedfrom an ionic compound-based catalytic metal precursor. Examples of anionic compound that can derive a negatively charged catalytic metalprecursor ion for producing a Pt catalyst include, but are not limitedto tetrachloroplatinic acid(II) (H₂PtCl₄), hexachloroplatinic acid(IV)(H₂PtCl₆), potassium tetrachloroplatinate(II) (K₂PtCl₄), potassiumhexachloroplatinate(IV) (K₂PtCl₆), or mixtures thereof.

Examples of an ionic compound that can derive a negatively chargedcatalytic metal precursor ion for producing a Ru catalyst include(NH₄)₂[RuCl₆] and (NH₄)₂[RuCl₅H ₂O].

Examples of an ionic compound that can derive a negatively chargedcatalytic metal precursor ion for producing an Au catalyst includeH₂[AuCl₄], (NH₄)₂[AuCl₄], and H[Au(NO₃)₄]H₂O.

For an alloy catalyst, a mixture of the catalytic metal precursorshaving a mixing ratio corresponding to a ratio of metal atoms as desiredcan be used.

Examples of a solvent in which the ionic compound is dissolved includewater, alcohol, acetone, and mixtures thereof. Examples of alcoholinclude, but are not limited to methanol, ethanol, and propanol.

The amount of each component in the mixture of support material havingthe polymer ion adsorbed thereon with the negatively charged catalyticmetal precursor ion is not specifically limited. However, if the amountof the support material having the polymer ion adsorbed thereon is toolow, the yield of the final product may be low. If the amount of thesupport material having the polymer ion adsorbed thereon added to themixture is too high, it becomes difficult to disperse the supportmaterial. Considering these factors, the amount of the support materialhaving the polymer ion adsorbed thereon added to the mixture may betypically range from about 0.2% to about 0.3% by weight based on theweight of total solvents in the mixture. Generally, the catalytic metalprecursor is added to the mixture in such an amount that the weightratio of Pt to the carbon support material is about 3:7.

While the mixture of the support material having the polymer ionadsorbed thereon with the negatively charged catalytic metal precursorion-containing solution is being stirred, the stirring time is notspecifically limited. The stirring time can vary depending on processconditions, such as performance of a stirrer and amount of materials tobe added. However, if the stirring time is too short, the catalyticmetal precursor ion may be locally arranged around the polymer ion.While, there is no upper limit to the stirring time, generally, thestirring time ranges from about 1 hour to about 2 hours.

After the negatively charged catalytic metal precursor ion is adsorbedonto the surface of the support material having the polymer ion adsorbedthereon in this way, the adsorbed catalytic metal precursor ion isreduced to a catalytic metal in a reducing solution. The term “reducingsolution” refers to a liquid reducing agent that oxidizes itself toreduce a catalytic metal precursor ion to a catalytic metal, or asolution containing a reducing agent which oxidizes itself to reduce acatalytic metal precursor ion to a catalytic metal.

Examples of the reducing agent may include but are not limited tohydrazine, formaldehyde, formic acid, and polyol. Examples of polyol mayinclude but are not limited to ethylene glycol, glycerol, diethyleneglycol, and triethylene glycol.

The catalytic metal precursor ion adsorbed on the support material maybe reduced by mixing it with the reducing solution, by stirring it as inthe previous operation, or as a product obtained by filtering themixture.

The amount of each component in the mixture for the reduction reactionis not specifically limited. However, if the amount of the supportmaterial having the catalytic metal precursor ion adsorbed thereon addedto the mixture is insufficient, the yield may be low. If the amount ofthe support material having the catalytic metal precursor ion adsorbedthereon added to the mixture is too high, it is difficult to dispersethe support material. Considering these factors, the amount of supportmaterial having the catalytic metal precursor ion adsorbed thereon addedto the mixture may generally range from about 0.2% to about 0.3% byweight based on the weight of total solvents (including the reducingsolution) in the mixture.

In order to accelerate the reduction of the catalytic metal precursorion, it is preferable to heat the mixture. If a heating temperature ofthe reactant mixture is too low, the effect of accelerating thereduction reaction may be very slight. If a heating temperature of thereactant mixture is too high, the reduction reaction rate becomes toorapid, and thus, it is impossible to attain a uniform reduction.Considering this, the heating temperature of the mixtures for thereduction reaction may be typically range from room temperature (i.e.,about 20° C.) to about 380° C. More preferably, the mixtures for thereduction reaction may be heated in such a range that a solvent in themixture for the reduction reaction (including the reducing solution) mayboil.

In addition, the reduction time is not specifically limited and it mayvary depending on process conditions such as the temperature of thereactant mixture. However, if the reduction time is too short, thefraction of unreduced support material may be increased. There are noupper limits to the reduction time but generally, the reduction time mayrange from about 1 hour to about 2 hours.

By reducing the catalytic metal precursor ion adsorbed on the surface ofthe support material in this way, the resulting catalytic metalparticles with an average particle size of from about 1.8 to about 4.5nm are uniformly formed on the surface of the support material.

Another exemplary embodiment of the present invention, provides a methodfor preparing a supported catalyst where a positively charged supportmaterial is first mixed with a negatively charged polymer ion-containingsolution to adsorb the polymer ion on the support material. Next, thesupport material with the polymer ion adsorbed on it is mixed with apositively charged catalytic metal precursor ion-containing solution toadsorb the catalytic metal precursor ion on the support material havingthe polymer ion adsorbed on it. Finally, the catalytic metal precursorion adsorbed on the support material having the polymer ion alsoadsorbed thereon is reduced to a catalytic metal in a reducing solution.

The surface of the support material may be positively charged byadjusting the pH of the dispersion in which the support material isdispersed. Examples of an anionic polymer ion used in the presentembodiment include, but are not limited to, poly(sulfopropylmethacrylate), poly(styrene sulfonate), polyacrylate and metal saltsthereof.

According to another embodiment of the present invention, there is ahighly-dispersed supported catalyst. The term “highly-dispersed” meansthat the average particle size of the catalytic metal particlessupported by the porous support material is much smaller than that of aconventional supported catalyst. The highly-dispersed supported catalystaccording to the present embodiment comprises a porous support material,a polymer electrolyte adsorbed on a surface of the porous supportmaterial, and a catalytic metal particle supported by the surface of theporous support material. The supported catalyst can be made using themethod according to the previous embodiment of the present invention.

In the supported catalyst according to the present embodiment, thesupport material, the polymer electrolyte, and the catalytic metal arethe same as those as described above. The amount of the polymerelectrolyte may range from about 4% to about 11% by weight based on thetotal weight of the porous support material. The amount of the catalyticmetal may be between about 8% to about 30% by weight based on the totalweight of the porous support material. The average particle size of thecatalytic metal particles may be between about 1.8 to about 4.5 nm.

The supported catalyst according to the present embodiment supports acatalytic metal particle having a reduced average particle size, andthus, the catalytic activity can be improved.

The supported catalyst according to the present embodiment can be usedin the catalyst layer of an electrode for a fuel cell. In addition, thesupported catalyst according to the present embodiment can be used as acatalyst for various chemical reactions, for example, hydration,dehydration, coupling, oxidation, isomerization, decarboxylation,hydrocracking, and alkylation, etc.

EXAMPLES Examples 1 through 5

Polyallylamine Hydrochloride (PAH)

0.5 g of graphite powders (XC72R-2800) were dispersed in 200 g ofdistilled water. PAH was dissolved in the graphite powder dispersion toproduce a first dispersion. The amounts of PAH added in Examples 1through 5 were 10, 20, 40, 60, 80% by weight, based on the weight of thegraphite powders, respectively.

0.550 g of H₂PtCl₆ was dissolved in 50 g of distilled water to produce asecond solution. Then, the second solution was added to the firstdispersion and was stirred for one hour.

0.504 g of NaBH₄ was dissolved in 13.32 g of distilled water to producea reducing solution.

The reducing solution was then slowly added to the mixture of the firstdispersion with the second solution, while being stirred for one hour toobtain a Pt/C supported catalyst.

The obtained Pt/C supported catalyst was filtered, washed, and thendried.

Examples 6 through 10

polyethylenimine (PEI)

Pt/C supported catalysts were produced in the same manner as in Examples1 to 5, except that PEI was used instead of PAH and that the amounts ofPEI added in Examples 6 through 10 were 10, 20, 40, 60, 80% by weightbased on the weight of the graphite powders, respectively.

Comparative Example: No Polymer Electrolyte Used

0.5 g of graphite powders (XC72R-2800) were dispersed in 200 g ofdistilled water to produce a first dispersion. 0.550 g of H₂PtCl₆ wasdissolved in 50 g of distilled water to produce a second solution. Then,the second solution was added to the first dispersion and stirred forone hour. 0.504 g of NaBH₄ was dissolved in 13.32 g of distilled waterto produce a reducing solution. The reducing solution was slowly addedto the mixture of the first dispersion with the second solution, whilebeing stirred for one hour to obtain a Pt/C supported catalyst. Theobtained Pt/C supported catalyst was filtered, washed, and then dried.

Evaluation Results

The amounts of polymer electrolyte in the supported catalysts producedin Examples 1 through 10 and Comparative Example were measured using athermogravimetric analyzer (TGA) and a differential scanning calorimeter(DSC). The results are shown in Table 1.

In addition, X-ray diffraction (XRD) analysis was performed for each ofthe supported catalysts produced in Examples 1 through 10 andComparative Example. The results are shown in FIG. 1 (Examples 1 through5) and FIG. 2 (Examples 6 through 10).

An average particle size of the supported Pt particles was determinedusing the XRD analysis results for the supported catalysts produced inExamples 1 through 10 and Comparative Example. The results are shown inTable 1.

TABLE 1 Amount of Average the polymer particle electrolyte in the sizesupported catalyst of the Polymer electrolyte (mg/g-supported supportedPt Sample name used material) (nm) Example 1 PAH, 10% by 4 4.5 weightExample 2 PAH, 20% by 5 4.5 weight Example 3 PAH, 40% by 7 3.9 weightExample 4 PAH, 60% by 6 3.9 weight Example 5 PAH, 80% by 8 3.7 weightExample 6 PEI, 10% by weight 4 4.7 Example 7 PEI, 20% by weight 5 4.5Example 8 PEI, 40% by weight 7 2.9 Example 9 PEI, 60% by weight 11 1.8(result of TEM) Example 10 PEI, 80% by weight 11 1.8 (result of TEM)Comparative No No 6.7 Example

Table 1 confirms that the average Pt particle size of each supportedcatalyst produced in Examples 1 through 10 is much smaller than that ofthe supported catalyst produced in Comparative Example without using apolymer electrolyte. Further, Table 1 confirms that the amount of thepolymer electrolyte used is inversely proportional to the average Ptparticle size.

The method according to an embodiment of the present invention providesa highly-dispersed supported catalyst containing a catalytic metalparticle with a reduced average particle size. The highly-dispersedsupported catalyst according to an embodiment of the present inventionhas an improved catalytic activity for the amount of catalytic metalsupported.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method for preparing a supported catalyst, comprising: mixing anegatively charged support material with a positively charged polymerion-containing solution to adsorb the polymer ion onto the supportmaterial; mixing the support material having the polymer ion adsorbedthereon with a negatively charged catalytic metal precursorion-containing solution to adsorb the catalytic metal precursor ion onthe support material having the polymer ion adsorbed thereon; andreducing the catalytic metal precursor ion adsorbed on the supportmaterial having the polymer ion adsorbed thereon to a catalytic metal ina reducing solution.
 2. The method of claim 1, wherein the negativelycharged support material is a carbon-based porous support material,SiO₂-based porous support material, TiO₂-based porous support material,or V₂O₅-based porous support material.
 3. The method of claim 2, whereinthe carbon-based porous support material is carbon black, carbonmolecular sieve, or carbon nanotube.
 4. The method of claim 1, whereinthe positively charged polymer ion is derived from a cationic polymerhaving a nitrogen atom in its backbone or branch.
 5. The method of claim1, wherein the positively charged polymer ion is derived from a compoundselected from the group consisting of polyallylamine hydrochloride,polyethylenimine, polydiallyldimethylammonium chloride,polymethacryloxyethyltrialkylammonium halide, aminoethylatedpolyacrylamide, Hofman-degradated polyacrylamide, polyethyleneamine,cationized starch, chitosan, poly L-lysin (PLL), pAMEAMA dendrimer,poly(L-glutamic acid) (PLGA), poly(1-methyl-2-vinylpyridine) (PVP), polyL-ornithine, polyspermine, diethylaminoethyl dextran (DEAE dextran), andmixtures thereof.
 6. The method of claim 1, wherein the polymer ion isderived from a polymer electrolyte having a weight average molecularweight in the range of 50 to 15,000.
 7. The method of claim 1, whereinthe catalytic metal precursor ion is an atomic group comprising Pt, Ru,Au, Pd, Rh, Ir, or Os, or mixtures of the atomic group.
 8. The method ofclaim 1, wherein the reducing solution may be selected from the groupconsisting of hydrazine, formaldehyde, formic acid, and polyol.
 9. Themethod of claim 1, wherein the reduction of the catalytic metalprecursor ion is performed at a temperature ranging from roomtemperature to 380° C.